It appears that the source package is simply incomplete as far as I can tell.
There are many Design project references which are broken (the two dlls being: Microsoft.Windows.Design.Extensibility.dll and Microsoft.Windows.Design.Interaction.dll).
As you can see here in the csproj file it appears to be referencing an "MS Design" folder in the solution root:
This "MS Design" folder is not in the root and isn't included anywhere in the zipped up source package.
Its also noted that the only assemblies that I can find on my system are for versions 126.96.36.199 and 188.8.131.52.
What am I missing here to compile the Silverlight libraries? Also on a side note: what is a DataVisualization.sln for? Is there documentation on how to compile it correctly? I appreciate any help getting this up and running -- Thanks!
Those Design projects are not necessary in order to build the Silverlight controls. They also require specific versions of Visual Studio to be installed on the machine. The Silverlight source code for the version you specificed has design projects for VS2010 and VS2012. I have VS2010 installed on my machine but I do not have VS2012 installed. The 2010 design project is able to find the Microsoft.Windows.Design assemblies automatically by looking in the VS2010 directory: c:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PublicAssemblies\Microsoft.Windows.Design.Extensibility.dll
But since I don't have 2012 installed the 2012 Design project can't find the assemblies it needs so it fails to build. If all you need to do is build the source so that it generates the control DLLs then I recommend that you unload the Design projects from the solution. They are not necessary for building the controls.
The DataVisualization solution just contains the data visualization controls such as XamDataChart, XamMap, XamLinearGauge, etc. It does not include the line of business controls. Infragistics.Silverlight.sln contains all of the Silverlight controls, DV and LOB.